NEW YORK (Reuters) - Large U.S. companies boosted their offshore earnings by 15 percent last year to a record $1.9 trillion, avoiding hefty tax bills by keeping the profits abroad, according to a new report.

The overseas earnings stockpile has climbed by 70 percent over the past five years, said research firm Audit Analytics. Data in its report covers the Russell 3000 index of the largest U.S. corporations.

U.S.-based multinationals do not have to pay U.S. corporate income tax on foreign earnings as long as the earnings do not enter the United States. Accounting rules also let the companies avoid recognizing a tax expense if management intends to keep the earnings indefinitely reinvested overseas.

"It would probably be nice to have this money in our country being used in our economy, but at the moment we see it growing elsewhere," said Don Whalen, general counsel and director of research at Audit Analytics.

Conglomerate General Electric Co , had the most indefinitely reinvested overseas earnings, at about $108 billion, while drugmaker Pfizer Inc was next with $73 billion, according to Audit Analytics.

Businesses have been lobbying Congress for a new law that would let them bring foreign profits home on a regular basis with little or no tax due, or for a one-time "tax holiday" on foreign earnings.

Most Democrats oppose a tax holiday on overseas profits, citing studies showing that a tax holiday enacted under former President George W. Bush did bring profits into the country, but that money was not widely used for hiring or capital investment.

Some tax activists have argued for repealing the tax deferral law that lets corporations park profits offshore tax-free, though this proposal has made little political headway.

Some companies have been borrowing money in the U.S. bond market rather bring their overseas earnings home.

Computer giant Apple Inc last week raised $17 billion in a record U.S. bond sale to help fund its plan to return money to its shareholders. The bond sale let Apple avoid taxes that would have been due if it had used some of its $102 billion in foreign cash instead.

Microsoft Corp , the world's largest software company, sold $2.7 billion in the bond market last month. It has about $74 billion of cash and short-term investments, but most of that is held outside the United States.